**Silage Contribution to Aflatoxin B1 Contamination of Dairy Cattle Feed**

Alonso V.A.1,2, González Pereyra M.L.2, Armando M.R.2, Dogi C.A.2, Dalcero A.M.1,4, Rosa C.A.R.5,6, Chiacchiera S.M.3,4 and Cavaglieri L.R.1,4 *1Departamento de Microbiología e Inmunología, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Cuarto, Córdoba, 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 3Departamento de Química, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Cuarto, Córdoba, 4Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 5Departamento de Microbiologia e Imunología Veterinaria, Universidade Federal Rural do Rio de Janeiro, Instituto de Veterinaria, Rio de Janeiro, 6Conselho Nacional de Pesquisas Científicas (CNPq), 1,2,3,4Argentina 5,6Brazil* 

#### **1. Introduction**

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Dairy production systems have traditionally relied on direct utilization of pastures and annual soiling crop. This feeding strategy is complemented by the use of other feeds such as grains, balanced feed, silage, hay and industrial products, the level of use was variable and it defined in any way the degree of intensification of each dairy production systems.

Over recent decades, this intensification has been increasing at an accelerated rate, partly because the farms that remain, integrated into general agricultural-livestock mixed models, increasing land for agriculture, as a result of best price-cost and simplicity of production. This change in management practices in dairy cattle breeding, from the extended to semiintensive or intensive form, has meant a change in the way animals are fed.

The change from grazing over large areas of land to cowshed feeding with grain-based concentrates and silage has greatly improved productivity increase on the number of animals per hectare and, in turn, improved performance and milk production per cow due to the nutritional advantages afforded by the new way of eating. The dairy industry has been driven to higher levels of efficiency and competitiveness. This management system makes storing feed necessary as it is used throughout the year whether it is produced in the same establishment or not. This raises the concern to protect these products from damage by insects, pests and fungal contamination in order to maintain an appropriate level of feed security. Storage systems for feed, both silage and whole grains are a man-made ecosystem in which quality and nutritive changes occur because of interactions between physical, chemical and biological factors.

The deterioration by fungi and mycotoxin contamination is one of the greatest risks of stored feed. Apart from reducing palatability and feed consumption, fungal growth leads to loss of nutrients and dry matter causing in animal performance (O´Brien et al., 2005). Fodder, cereals

Silage Contribution to Aflatoxin B1 Contamination of Dairy Cattle Feed 39

Figure 1 shows estimated components proportion, which may vary slightly according to season and geographical area. Perennial pastures are usually based on alfalfa pasture. Forages are used both for direct consumption of pasture (winter and summer soiling) and as conserved forage in the form of rolls or bales of hay. Typically, 10% of forage is intended for these purposes and often rye, oats, moha, wheat and sorghum are selected in dairy farms according to acreage and selected pasture. As concentrates, grain corn, grain sorghum, cotton seed, wheat bran, dregs of malt, peanut shells, and sunflower expeller, are used

Corn (*Zea mays* L.) is the most widely grown crop in the Americas, extensively used for animal feeding and human consumption due to its nutritional value. A large percentage of the world corn production is destined to animal feeding. Silage is a widespread practice to preserve forages during extended time periods. The production of corn silage entails incorporation of the whole plant and its storage is based on the principle of preservation under anaerobic conditions with growth of lactic acid bacteria which promote a natural fermentation that lowers the pH to a level at which clostridia and most fungal growth are inhibited. In dairy cows, silage is a preferred food by the vast

Grazing

56%

As corn silage consists of grinding and storing the whole corn plant, it includes not just grain but a high percentage of stalks and stover and represents a new important bulky feed source for dairy and beef cattle. Nutritionally, corn silage, for example, has a balance between the energy density of the grain and fibber and digestibility of the green plant that makes it suitable for feeding ruminants in the phases of maximum nutritional needs (Molina

Silage is a method of forage preservation based on lactic acid fermentation, usually spontaneous under anaerobic conditions, where the pH reaches values of 2-3 being an important indicator of forage conservation (Johnson et al., 2002). Air must be removed as much as possible from the silo in order to obtain good silage quality. To achieve this goal, certain management aspects must be emphasized. Forage should be harvested, chopped,

among others. It is also common to use commercial pelleted feed.

Fig. 1. Typical diet for milking cows (Chimicz & Gambuzzi 2007).

17%

Reserves

27%

Concentrate

**3. Corn silage** 

majority of producers.

**4. Ensiling and storage conditions** 

et al., 2004).

and seeds used in feed for dairy cattle are naturally in contact with yeasts and filamentous fungi, the contamination of raw materials occurs frequently in the field, because of the infection of plant symbiotic fungi as phytopathogens. This contamination can also occur during harvesting, transport and storage of these products and post harvest mishandling can lead to rapid spoilage. In well-preserved forages fungal growth depends on moisture conditions of the plant during harvest. Stored feed, moisture, temperature and oxygen availability are key conditions that determine risk degree of fungal contamination. The critical water activity for safe storage is 0.7 to 0.8 (Magan & Aldred 2007; Scott, 1957). When this level is exceeded, large degrading ability fungi as *Eurotium sp.*, and species of *Aspergillus* and *Penicillium* can grow. Increase in respiratory activity, due to the development of these fungi, leads to an increase in the temperature of feed that can lead to the contamination by other fungi especially thermophilic fungi and, therefore, to further deterioration.

Silage is one of the main constituents in the diets of dairy cattle and its deterioration and aflatoxin contamination can lead to considerable production losses and a major impact on human health.

#### **2. Breeding and feeding systems on dairy farms**

In many systems of milk production mainly in the northern hemisphere, the dairy cows are housed in stockyard due to extreme weather conditions, either high or low temperatures. These intensive production systems use a minimal proportion of grass per cow. In other systems, where climates are more benign and temperate, the production system is typically extensive grazing.

In general, worldwide, the diversity of soils, climates and production scales do not allowa single production system; it is clear that there has been a gradual shift from purely pastoral models to semi-intensive systems (López 2008). In the first instance, the producers began to incorporate ration, preferably, corn grain or commercial feed and for this, they took the shackles of milking, where feeders are installed. Simultaneously, the corn silage began to spread, both as a reserve fodder as well as balanced diet. At this point, producers required new ways of providing meals.

This intensification is necessarily accompanied by a significant increase of the scale, this fact causes many people to use new technologies to keep the cows in confinement.

The development in milk production in recent years has followed an intensification which has resulted in a change in the use of feed, evolving from simple grazing feeding systems based on mixed feed formulation combining grains and forages.

Although the current systems of feeding in major milk producing areas in Argentina have particular differences in the degree of intensification, they can be considered supplement grazing systems (or semi-intensive). Through this enhancement, production level was able to grow extensively. The levels of milk production increased from 12 L to 20-30 L. However, animal numbers by hectare did not increase. That supplementation can not only avoid the seasonality of production due to the availability of pastures in different seasons, but also allow to balance the dietary components optimizing milk production per cow (West, 2003). However, many authors argue not to forget grass, which remains the staple feed "of ruminant herbivores" as well as the cheapest cost of production.

The composition of feed rations for dairy cows consists of:


Figure 1 shows estimated components proportion, which may vary slightly according to season and geographical area. Perennial pastures are usually based on alfalfa pasture. Forages are used both for direct consumption of pasture (winter and summer soiling) and as conserved forage in the form of rolls or bales of hay. Typically, 10% of forage is intended for these purposes and often rye, oats, moha, wheat and sorghum are selected in dairy farms according to acreage and selected pasture. As concentrates, grain corn, grain sorghum, cotton seed, wheat bran, dregs of malt, peanut shells, and sunflower expeller, are used among others. It is also common to use commercial pelleted feed.

Fig. 1. Typical diet for milking cows (Chimicz & Gambuzzi 2007).
